1. Field of the Invention
This invention relates to aircraft. Particularly, this invention relates to fuel tank systems for aircraft.
2. Description of the Related Art
It has been proposed that aircraft will eventually transition to hydrogen fuel for increased efficiency and to reduce emissions. Hydrogen as fuel is more efficient, offering higher energy content per mass. Accordingly, hydrogen promises increased payload and range for aircraft. In addition, hydrogen offers benefits in terms of emissions because it can be produced by electrolysis of water and produces water when it is burned.
FIG. 1 illustrates the volume and mass relationships between gaseous and liquid hydrogen and typical jet fuel. Hydrogen weighs nearly one third as much as typical jet fuels (e.g., kerosene fuels) for an identical amount of energy content. However, hydrogen cooled to a liquid state in high pressure tanks requires approximately four times the volume as kerosene fuels.
Over the years progress has been made in developing the concept of hydrogen fueled aircraft. In 1937, Dr. V. Ohain tested a He—S-2 experimental turbojet engine on hydrogen. The Tupolev Tu 155 laboratory aircraft proved the feasibility of transport aircraft flying on liquid hydrogen and liquid natural gas (LNG) in 1988. In addition, since 1955 multiple studies have been performed by NASA, the U.S. Air Force, Boeing and Lockheed as well as foreign interests (e.g., Germany and Russia). For example, in 1957, U.S. Air Force B-57 bomber flight tests were performed.
However, prior attempts to develop viable aircraft using hydrogen fuel have faced difficulties. For example, prior designs provided an insufficient fuel volume to support a useful payload or acceptable mission range. Also, inefficient aerodynamic shapes typically resulted having large frontal and surface areas. Multiple small tanks with multiple domes added too much additional weight. In addition, fuel tanks may be placed in the path of engine rotor burst trajectory. Additional fuel storage displaces areas typically used for passengers or payload, decreasing the overall utility of the aircraft. Thus, the objective of producing a hydrogen powered aircraft configuration that combines the required fuel volume within an aerodynamically efficient shape, minimizes hydrogen tank weight penalty, and still maintains usable space for aircraft functionality and utility has not been met. Separately, blended wing body aircraft designs have been previously developed, but without focusing on their application to hydrogen fuel aircraft.
U.S. Pat. No. 6,568,632, by Page et al. and issued May 27, 2003 discloses a blended wing body aircraft having a modular body. In one embodiment, the configuration or cargo capacity of the aircraft can be varied by adding or subtracting intermediate body structures rather than by adding or subtracting segments from the lateral sides of the aircraft body. Configuration in this manner preserves key aerodynamic parameters and permits several major components to be used in several aircraft configurations, each of which having a different cargo capacity. In another embodiment, the aircraft is formed from a plurality of laterally-extending body structures. Changes to the cargo capacity of the aircraft is accomplished through the employment of body structures that are wider or narrower. Configuration in this manner provides the aircraft with a structure that is relatively strong and efficient. While the body structures of this embodiment are not shared across a family of variously sized aircraft, the base design of the body structures is readily modifiable to adjust for an increase or decrease in width associated with a desired change to the aircraft's cargo capacity.
U.S. Pat. No. 6,666,406, by Sankrithi et al., issued Dec. 23, 2003, discloses a partial blended wing body airplane configuration combining the advantages of a pure blended wing configuration with the advantages of conventional aircraft design. A blended tri-body airplane configuration wherein three pressurized body elements are connected by and blended with a pressurized centerwing element. The sidebodies and centerbody are blended into the wing structure, producing a multi-body airplane whose body sections are interconnected utilizing wing payload carrying sections.
U.S. Pat. No. 6,708,924, by Page et al., issued Mar. 23, 2004, discloses a blended wing body aircraft having a modular body having a body that includes a plurality of laterally-extending body structures. Changes to the cargo capacity of the aircraft is accomplished through the employment of body structures that are wider or narrower. Configuration in this manner provides the aircraft with a structure that is relatively strong and efficient. While the body structures of this embodiment are not shared across a family of variously sized aircraft, the base design of the body structures is readily modifiable to adjust for an increase or decrease in width associated with a desired change to the aircraft's cargo capacity.
U.S. Pat. No. 5,909,858, by Hawley, issued Jun. 8, 1999, discloses a blended wing-body aircraft includes a central body, a wing, and a transition section which interconnects the body and the wing on each side of the aircraft. The two transition sections are identical, and each has a variable chord length and thickness which varies in proportion to the chord length. This enables the transition section to connect the thin wing to the thicker body. Each transition section has a negative sweep angle.
U.S. Pat. No. 5,893,535, by Hawley, issued Apr. 13, 1999, discloses structural ribs for providing structural support for a structure, such as the pressure cabin of a blended-wing body aircraft. In a first embodiment, the ribs are generally “Y-shaped”, being comprised of a vertical web and a pair of inclined webs attached to the vertical web to extend upwardly and outwardly from the vertical web in different directions, with only the upper edges of the inclined webs being attached to a structural element. In a second embodiment, the ribs are generally “trident-shaped”, whereby the vertical web extends upwardly beyond the intersection of the inclined webs with the vertical web, with the upper edge of the vertical web as well as the upper edges of the inclined webs being attached to the same structural element.
In view of the foregoing, there is a need in the art for hydrogen powered aircraft configurations that combine the required fuel volume within an aerodynamically efficient shape. There is also a need for such aircraft designs that minimize hydrogen tank weight penalty and still maintain usable space for aircraft functionality and utility. These and other needs are met by the present invention as detailed hereafter.